Carbon pile device



June I, 1954 T. w. MOORE CARBON PILE DEVICE 2 She'ets-Sheet 1 FiledApril 10, 1951 Z 0 0 1 7 6 R 4! N 8 O R W m 0/ m m 4 6m I mw 7 w 6 M I-8 5 I k 6. W. I w 5 \s 8 THOMAS W. MO R ATTORNE YS 'Illlli J 1, 1954 T;w. MOORE 2,680,176

CARBON PILE DEVICE Filed April 10, 1951 2 Sheets-Sheet 2 INVEN TORTHOMAS W Moo/2E BY A TTORNEYS Patented June 1, 1954 CARBON PILE DEVICEThomas W. Moore, Dayton,

Ohio, assignor, by

mesne assignments, to American Machine &

Foundry Company,

New York, N. Y., a corporation of New Jersey Application April 10, 1951,Serial No. 220,290

25 Claims. 1

This invention relates to carbon pile devices and to electromagneticmeans for effecting actuation thereof.

It is the principal object of the invention to provide anelectromagnetically actuated carbon pile device which is simple andeconomical in construction, which can be readily assembled and whichwill provide operating characteristics that are un' orm and readilyadjustable, and which will maintain a high degree of accuracy anduniformity in operation even though subjected to severe jolts Ormechanical shocks and notwithstanding wide changes in temperature.

It is a further object to provide an electromagnetic device having anarmature and a pole piece which are accurately located relative to eachother for high reliability and uniformity throughout operation.

t is a further object to provide a core and pole piece assembly for anelectromagnetic device in which the pole piece comprises two portions ofmagnetic material spaced from each other to form a non-magnetic gap withthe entire surface thereof plane and highly uniform and in accuratenormal relation to the axis of the core.

It is also an object to provide a simple and highly satisfactory methodof forming such a core and pole piece assembly.

Other objects and advantages will be apparent from the followingdescription, the accompanying drawings and the appended claims.

In the drawings- Fig. 1 is a view partially in section and partially inelevation of an electromagnetically operated carbon pile deviceconstructed in accordance with the present invention;

Fig. 2 is a horizontal sectional view on the line 2-2 of Fig. l with thesolenoid shown in elevation;

Fig. 3 is a horizontal sectional view of Fig. 1 through the pile andradiator on the line 3-3 of Fig. 1;

Fig. 4 is a vertical sectional view on an en-- larged scale of theelectromagnetic part of the device with parts broken away to furthershow the construction;

Fig. 5 is a top plan parts broken away;

Fig. 6 is a detailed broken sectional view showing the hingeconstruction and the parts which limit the travel of the armature online 6-6 of Fig. 5;

Fig. 7 is a detail view of the means for adjusting the initial pressureon the carbon pile;

Fig. 8 is an exploded perspective view of the parts forming the armatureassembly;

view of the armature with Fig. 9 is a vertical sectional view on anenlarged scale through the lower portion of the pile and radiator,further showing the lower contact assembly;

Figs. 10 through 12 are vertical sectional views showing the steps inthe construction of the pole piece and core assembly;

Fig. 13 is a plan view piece;

Fig. 14 is a bottom assembly;

Fig. 15 is a detail l5l5 of Fig. 14; and

Fig. 16 is a top plan view of the lower contact assembly.

Referring to the drawings which show a preferred embodiment of theinvention, the carbon pile is shown generally of relatively thin disksof carbon, preferably having a central aperture therein, which arestacked in a tubular member material having proper strength and capableof operation at elevated temperature. A suitable ceramic material forthis purpose is that known as Steatite, although other comparablematerials may likewise be used. The tube is of the proper internaldiameter to receive the carbon disks freely therein and the stack is ofsuch length as to leave a projecting portion of the ceramic tube ateither end thereof.

of the face of the pole view of the lower contact sectional view on theline provided, and to increase the radiating effect, the device isfinned as shown at It. As illustrated in Fig. 9, the fins are of steppedwidth, there being a narrower internal cut-out I? with a wider outerportion l8 forming such steps. These fins are preferably formed byturning a solid bar of the material in a lathe and performing two cuts,the inner and deeper one being narrower than the outer cut, therebymaking possible the formation of such deep cuts and maintaining goodheat transfer and physical strength characteristics throughout. Asuitable material for the radiator is one which has good heat conductingqualities, and where weight is a factor, both properties are wellprovided by the use of aluminum.

In order to provide for expansion and contraction of the radiator, andto maintain the same in close heat transferring relation with theceramic tube throughout such temperature changes the radiator isprovided with an axial cut shown at 20 which extends throughout itslength. The internal bore of the radiator is such that it normally mustbe spread in order to be at l 0 consisting of a series I2 of ceramic orlike received. over the ceramic tube l2, and when so positioned it gripsthe tube due to its resiliency and thus is in close heat transferringcontact therewith. As the diameter of the tube changes under variationsof temperature, the radiator body expands or contracts sufficiently toremain in such gripping contact, and thus there is no decrease in' theheat conducting properties thereof as the dimensions of the tubeincrease or decrease.

Electric contact is made with the lower end of the pile by an insulatedcontact assembly shown in Figs. 9 and 14 through 16. The contact itselfis in the form of a thin lamination'of silver 26 mounted upon a backing27' of Monel metal, which in turn is secured to a contact element 2%having a lug 29 extending outwardly therefrom. The assembly is carriedby an insulating plate Bil of laminated silicon fiber glass or the like,the entire structure being secured by means of a central rivet 32 havinga spring washer 33 on the lower face of the insulating member to retainthe assembled structure together. It will be seen that the head of therivet 32 is located in the central aperture of the carbon disks with theface of the disks seating directly upon the contact surface 245 and thusgoo-:lelectrical contact is maintained. A prong 3% may be struck into anaperture in the insulating plate toprevent twisting therebetween afterassembly.

The insulating plate 33 is seated in a cover plate 35 of suitablematerial such' as stainless steel, being mounted diagonally therein asshown in Figs. 14: and 16 in an offset portion 36 and secured therein bya pair of rivets 3'5. The cover plate isheld in place by four studshaving nuts 3E5 by means of which the cover plate is secured in positionwith the contact member 28 being drawn against the lower end of theceramic sleeve i2 to properly locate the lower contact assembly.

In order to secure accuracy of control with such a device it isimportant that the pole piece of the electromagnet be positioned withaccuracy relativeto the core and also relative to the armature, so thatthe movements of the armature will talce'place uniformly and with theair gap being substantially uniform in' all relative positions thereof.It is also important that" the magnetic parts of the structure, whichare usually formed of iron subject to rapid rusting and corrosion, beplated for use, and that such plating operationnot interfere with properaccuracy of alignment or result in introduction of non-uniform anddisturbing factors into the operating characteristics. In accordancewith the present invention, therefore, the pole piece is constructed inaccordance with the steps indicated in Figs. 10 through 13. Referringfirst to Fig. 10, a body of magnetic material 38 in the form of a flatplate is formed with an annular groove H on one face having a tapered orconical section as shown, and with a tapered aperture 32 having itslarger width on the opposite face. It should be particularly noted thatthe groove ll extends only partially through the body from the facethereof, leaving an integral section 43 on the opposite face.

A core member 45 is provided with a central bore 45 and located inposition on the grooved face of the body 40, centrally thereof, asindicated in Fig. 11. It is secured thereto in suitable manner such asby brazing, indicated at A? indicated in Fig. 12.

in a position substantially normal to the opposite or working face ofthe pole piece ill.

Non-magnetic material 5!; is introduced into the groove ll partiallyfilling the same and bon ing firmly to the side walls of the grooves. Asuitable material for this purpose is a ring of brazing material, andsuch material may likewise be used to bond the core 45 in position uponthe face of member 40 and thus both operations may be performed at thesame time.

Thereafter the assembly is suitably supported by means of the core 45and material is removed from the working face of the body ill to a depthsuch as to cut through the integral section 43 and into the body ofnon-magnetic material 58. It will be seen that by removing more materialfrom the surface, the non-magnetic gaps indicated at 52 are increased inwidth, and vice versa, while at all times assuring that the surfacewhich will form the actual pole face is plain, flat, and accuratelynormal to the axis of the core. This operation is convenientlyaccomplished by chucking the core in a lathe and cutting across the faceof member M3 to the required depth as The finished piece then has theappearance in plan as shown in Fig. 13 with an annular gap 52 ofnon-magnetic material separating the two magnetic portions and retainingthem permanently in flat and plane relation to each other.

The pole face and core assembly is then assembled with the solenoidindicated at El) and a bottom magnetic plate 62 is fitted over the endof the core as shown in Fig. 4. It is preferred to have a close fit withthe core projecting beyond the lower face of the plate 62 as shown at fil and capable of relative sliding movement through the plate, althoughwith as small an air gap as possible. Thus assembly is facilitated andlikewise some axial movement is permitted between these parts inresponse to thermal xpansion and contraction but without materiallyincreasing the reluctance of the magnetic circult.

The magnetic structure is completed means of a series of posts 55, heldin assembled relation upon the lower magnetic plate 62 by means ofthreaded extensions 56 formed part of the studs 38. As shown in Fig, ithe posts are bored and tapped to receive the threaded ends 35 and theremaining section of magnetic ma ial is such as to provide substarniallyunifo density throughout the magnetic circu posts 65 are preferablyground accuratel to uniform length and thus the upper ends when mountedupon the plate 62 are all accui ely in the same plane and adapted toengage to support pole piece it in accurate 1 thereto.

The pole piece is held in place upon the posts by means of two pairs ofbolts, an outer pair ill carrying collars "l2, and an inner pair is likewise having collars l5 thereon.

The armature assembly is composed of fiat plate-like members'which maybe readily manufactured in flat condition and subjected to suitable heattreating toassure the absence of d' tortions or strains, so that theassembly maintain its fiat characteristic notwithstanding changes intemperature and the like during use. The assembly comprises the armatureplate til which is of generally corresponding dimensions with pole piece40, having notched out areas 31 at the forward end thereof which areadapted to fit under the headed part of collars 12, as

shown in Fig. 6, the latter to prevent excessive forming limit stopstravel of the armature. Plate Bil has a part 32 extending rearwardlybeyond the pole piece 40 and a thin sheet metal hinge spring 85 issecured to the lower face of this portion of the armature plate, suchhinge 85 having forwardly extending projections or ears 86 apertured at87 to be received over the rearward pair of studs 1 t. The armatureplate til is notched out as shown at 88 to provide clearance for theseforwardly projecting portions dd. Also as shown in Fig. 6, collars areadapted to seat downwardly upon the face of projections so that when therear bolts 14 are tightened, the hinge spring 85 is secured in directposition upon the flat face of the pole piece le. Also as shown thehinge member 85 is relatively thin and thus the lower face of thearmature ilil is substantially parallel to but spaced slightly away fromthe face of pole piece 40.

The spring hinge 85 is secured to the armature plate 80 together with anupper fiat weight iii and a lower fiat weight 9!, rivets 92 securing allsuch parts together. The weights are of such size and location as tocounter-balance the mass of the armature about its hinge and thus tocompensate for such shocks or vibrations as may occur in the planenormal to the face of the armature. It will also be noted by referenceto Figs. 4 and 5 that the hinge for the armature is actually formed bythe two spaced projecting portions 86 of the hinge plate immediatelyjacent the studs "M, and located substantially at the rear edge of thepole piece which thus forms a fulcrum for the armature. Except for theextensions 85, the hinge plate terminates along a line which fallsbeyond the edge of the pole piece and thus assures that the pivoting ofthe armature will take place about the two extensions of the spring andsubstantially in the plane of the cover plate itself. Movement of thearmature assembly is controlled at all times and it is assured that suchmovement will take place with the armature plate 80 maintaining uniformclearance from the pole piece, throughout its range of movement.

In order to provide a predetermined minimum pressure on the carbon pilesuihcient to prevent separation of the disks and burning under minimumor no magnetic pull, a spring device is provided by means of which thisminimum pressure condition may be adjustably established and maintained.For this purpose a groove lot is formed in the upper surface of armatureplate Bil, this groove being preferably arcuate in cross section asillustrated in Fig. 4. At its deepest point it closely approaches thelower face of the plate so that the force applied thereto will, asnearly as practicable, be effective in the same plane as that of thehinge means. The spring itself is in the form of a clip Hi2 havingslotted openings #03 at either end which are adapted to be received overthe pair of studs 7d above collars l5. A central downwardly bent portionEll has a depressed tongue I05 the tongue being in direct bearingengagement with the curved bottom surface of the groove. It will be seenthat the force applied by this spring is in the direction to causecompression of the pile and that by shifting the clip on its supportingstuds the moment arm of that force can be varied, to thereby change theinitial or minimum pressure condition. The arrangement of the parts asshown, including the angle of the tongue I05 and the arcuate surface ofthe groove I00 also contribute to maintenance of substantially uniformconditions compensating largely for any change in the effective forceapplied as a result of the travel of the armature plate.

lectrical contact is made and pressure applied to the top of the pile bymeans of a screw Ht which is threaded into an aperture in the center ofthe armature plate with a spring clip Iii (Fig. '7) welded or fastenedthereto which has friction portions H2 engageable on the surface of thearmature plate and which tend to retain the screw frictionally in anyadjusted position. In response to turning, the screw is raised orlowered with respect to the armature plate.

The lower end of the screw is cupped and the surface of the cuppreferably coated with a good electrical conductor such as silver forreceiving the upper end of a push rod H5, preferably of beryllium copperand the like and having a similar silver contact to establish goodelectrical conductivity. The push rod H5 extends through the centralaperture 46 of the core and projects from the lower end thereof where apressure contact H7 is fastened, in the form of a silver contact diskHi3 with a Monel backing disk H9. In this way operating pressure istransmitted to the top of the pile, the pull of the solenoid thus beingutilized to apply pressure to the pile to cause a lowering of theelectrical resistance thereof.

A dust cap i2!) is preferably clipped over the upper portion of thedevice, covering the armature assembly, and the posts 65 may be suitablydrilled as shown at |2l to serve to receive a mounting structure I22thereon by means of which the control may be mounted and the oppcsite orgrounded electrical connection made thereto.

In the construction of the device the parts of the magnetic circuit arepreferably first formed accurately as to size and shape, the posts 65being accurately ground or otherwise formed to uniform length and theflat parts of the pole piece and armature assembly suitably heat treatedunder stacking and pressure in order to assure annealing in a flatcondition. Thereafter, and before assembly into final form, the partsmay be electroplated in order to protect them against rusting and thelike, such electroplating not resulting in any distortion or deformationof the parts. When assembled following such plating, the parts retaintheir flat and accurately formed relationship, both as initiallyassembled, and during changes of temperature, rapid or severe shocks andthe like, to which the device may be subjected in use. Highlysatisfactory resuits have been obtained over a complete range ofoperating temperatures and over shock and vibration conditions up tomany times the force of gravity.

While the method and form of apparatus herein described constitutepreferred embodiments of the invention, it is to be understood that theinvention is not limited to this precise method and form of apparatus,and that changes may be made therein with-out departing from the scopeof the invention which is defined in the appended claims.

What is claimed is:

1. A carbon pile device comprising a solenoid, an armature for saidsolenoid, a carbon pile, means for transmitting pressure from saidarmsture to effect compression of said carbon pile, a tubular member forreceiving said carbon pile inwardly thereof, and a metallic radiator ofresilient construction having an internal diameter normally less thanthat of said tubular member surrounding said tubular member in closeheat transferring relation therewith, said radiator having alongitudinally extending slot therein and being expandable to receivesaid tubular member and to maintain said close heat transferring contactwith said tubular member under temperature changes.

2. A carbon pile regulator comprising a solenoid, an armature for saidsolenoid, a carbon pile, means for transmitting pressure from saidarmature to effect compression of said carbon pile, a tubular sleevemember of ceramic material for receiving said carbon pile inwardlythereof, and a metallic radiator of resilient construction having aninternal diameter normally less than that of said tubular membersurrounding said tubular member in close heat transferring relationtherewith, said radiator having a longitudinally extending sl-ot thereinand being expandable to receive said tubular member and to maintain saidclose heat transferring contact with said tubular member undertemperature changes.

3. A carbon pile device comprising a solenoid, an armature for saidsolenoid, a carbon pile, means for transmitting pressure from saidarms.- ture to effect compression of said carbon pile, a tubular memberfor receiving said carbon pile inwardly thereof, and a metallic radiatorsurrounding said tubular member in close heat transferring relationtherewith, said radiator having deep fins therein of stepped width andthe walls of each step being substantially parallel.

e. The method of making a pole piece for an electromagnetic device whichcomprises forming a groove in the face of and extending partiallythrough a body of magnetic material leaving an integral section thereof,placing nonmagnetic material in said groove in firmly bonded relationwith the surface of said groove, and thereafter removing material fromthe opposite face of said body of magnetic material beyond said integralsection leaving two portions of magnetic material spaced from and heldin accurate alignment with each other by an intervening section ofnon-magnetic material.

5. The method of making a pole piece for an electro-magnetic devicewhich comprises forming an annular groove in the face of andextendpartially through a body of magnetic material leaving an integralsection thereof, placing non-magnetic metallic material in said groovein firmly bonded relation with the surface of said groove, andthereafter removing material from the opposite face of said body ofmagnetic material beyond said integral section leaving two portions ofmagnetic material spaced radially from and held in accurate alignmentwith each other by an intervening section of said non-magnetic material.

6. In a carbon pile device, a carbon pile, a. solenoid, a flat polepiece in magnetic relation with said solenoid, an armature assemblycooperating with said pole piece and including a flat armature plate, aspring hinge member fastened to said plate in substantially the plane ofthe face thereof, means for mounting said hinge member upon said polepiece with said pole piece forming a fulcrum for said hinge member,means on the opposite side of the hinge axis of said hinge member fromsaid armature assembly for counterbalancing said assembly to compensatefor vibrational effects in the plane normal to said 8 armature, andmeans for transmitting the pull of said armature to said carbon pile toeffect compression thereof.

'7. The method of forming a magnetic device including a core and a polepiece in accurate align ment therewith comprising forming a groove inthe face of and extending partially through a body of magnetic materialleaving an integral section thereof, placing non-magnetic material insaid groove in firmly bonded relation with the surface of said groove,securing a core in assembled relation upon said body on the face thereofsaid groove, and thereafter supporting said assembly from said corewhile removing material from the opposite face of said body to a depthbeyond said groove leaving two spaced areas of magnetic materialseparated by said nonmagnetic material and in predetermined accuraterelation with said core.

8. The method of forming a magnetic structure including a core and apole piece in accurate alignment therewith comprising forming a groovein the face of and extending partially through a body of magneticmaterial leaving an integral section thereof, placing non-1nagneticmaterial in said groove in firmly bonded relation with the surface ofsaid groove, securing a core in assembled relation upon said body on theface thereof having said groove, and thereafter turning said assemblyabout the axis of said core while re moving material from the oppositeface of said body to a depth beyond said groove leaving spaced areas ofmagnetic material separated by said non-magnetic material and inpredetermined accurate relation with the of said core.

9. In a carbon pile device, a carbon pile, a solenoid, a flat pole piecein magnetic relation said solenoid, an armature assembly cooperatingwith said pole piece and including a flat armature plate, a thin springhinge member fastened to said plate, means for mounting said hingemernber upon said pole piece with the edge of se Ll. pole iece forming afulcrum forsaid hinge member, and means for applying a. biasing pressureto said armature plate in substantially the plane of said hinge memberin the same direction as the force developed by said solenoid toestablish a minimum pressure condition within said pile.

10. In a carbon pile device, a carbon pile, a so noid, a fiat pole piecein magnetic relation with said solenoid, an armature assemblycooperating with said pole piece and including a flat armature plate, a.spring hinge member fastened to said plate, means for mounting saidhinge member upon said pole piece with said pole piece forming a fulcrumfor said hinge member, means for applying biasing pressure to saidarmature plate in substantially the plane of said hinge member and inthe same direction as the force developed by said solenoid to establisha minimum pressure condition within said pile, and means for adjustingthe point of application of said biasing pressure relative to saidfulcrum to vary said mini mum pressure condition.

11. In a carbon pile device, a carbon pile, a solenoid, corner postsforming part of the magnetic circuit of said solenoid, a pole piecemounted on said corner posts and having a magnetic gap in the facethereof, an armature assembly cooperating with said pole piece andincluding a fiat armature plate, a spring hinge member secured to saidplate, means for fastening said hinge member to a pair of said cornerposts in position upon the face of said pole piece with said pole pieceforming a. fulcrum for said assembly.

12. In a carbon pile device, a carbon pile, a solenoid, corner postsforming part of the magnetic circuit of said solenoid, a pole piecemounted on said corner posts and having a magnetic gap in the facethereof, an armature assembly cooperating with said pole piece andincluding a flat armature plate, a spring hinge member secured to saidplate, said armature plate having clearance with respect to a pair ofsaid corner posts, and means for fastening said hinge member to saidpair of corner posts in position upon the face of said pole piece formovement of said plate relative to said pole piece.

13. In a carbon pile device, a carbon pile, a core of magnetic material,a solenoid on said core, corner posts forming part of the magneticcircuit of said solenoid, ner posts and having a non-magnetic gap in theface thereof, an armature assembly cooperating with said pole piece andincluding a. fiat armature plate, a spring hinge member secured to theface of said plate adjacent said pole piece, said hinge member havingspaced extensions adapted to be received in position on a pair of saidcorner posts, and means including said extensions for fastening saidhinge member in position directly upon the face of said pole piece withsaid pole piece forming a fulcrum for said assembly.

14. In a carbon pile device, a carbon pile, a core of magnetic material,a solenoid on said core, corner posts forming part of the magneticcircuit of said solenoid, a pole piece mounted on said corner posts andhaving a non-magnetic gap in the face thereof, an armature assemblycooperating with said pole piece and including a flat armature plate, aspring hinge member secured to the face of said plate adjacent said polepiece, said hinge member having spaced extensions adapted to be receivedin position on a pair of said corner posts, means including saidextensions for fastening said hinge member in position directly upon theface of said pole piece with said pole piece forming a fulcrum for saidassembly, a groove formed in the outer surface of said plate, andresilient means engageable in said groove for applying a biasingpressure to said armature.

15. In a carbon pile device, a carbon pile, a core of magnetic material,a solenoid on said core, corner posts forming part of the magneticcircuit of said solenoid, a pole piece mounted on said corner posts andhaving a non-magnetic gap in the face thereof, an armature assemblycooperating with said pole piece and. including a flat armature plate, aspring hinge member secured to the face of plate adjacent said polepiece, said hinge member having spaced extensions adapted to be receivedin position on a pair of said corner posts, means including saidextensions for fastening said hinge member in position directly upon theface of said pole piece with said pole piece forming a fulcrum for saidassembly, and means mounted on said pair of corner posts for applying abiasing pressure to the outer surface of said plate.

16. In a carbon pile device, a carbon pile, a core of magnetic material,a solenoid on said core, corner posts forming part of the magneticcircuit of said solenoid, a pole piece mounted on said corner posts andhaving a non-magnetic gap in the face thereof, an armature assemblycooperating with said pole piece and including a flat armature plate, aspring hinge member secured to the of said plate adjacent said polepiece, said hinge member having spaced extensions adapted to be receivedin position on a pair of said corner within said tubular l0 posts, meansincluding said extensions for fastenthe face of said pole piece withsaid pole piece forming a fulcrum for said assembly, and means mountedon said pair of corner posts for applying a biasing pressure to theouter surface of said plate, said groove having a curved surfaceproviding for adjustable contact with said resilient means.

17. In a carbon pile device, a carbon pile, a core of magnetic material,a solenoid on said core, corner posts forming part of the magneticcircuit of said solenoid, a pole piece mounted on said corner posts andhaving a non-magnetic gap in the face thereof, an armature assemblycooperating with said pole piece and including a flat armature plate, aspring hinge member secured to the face of said plate adjacent said polepiece, said hinge member having spaced extensions adapted to be receivedin position on a pair of said corner posts, means including saidextensions for fastening said hinge member in position directly upon theface of said pole piece with said pole piece forming a fulcrum for saidassembly, a groove formed in the outer surface of said plate, resilientmeans engageable in applying a biasing pressure to said armature, andmeans for adjusting the point of application of said resilient meansrelative to said fulcrum to vary the biasing pressure on said armature.

18. In a carbon pile device, a solenoid, an armature for said solenoid,a carbon pile, a tubular member for receiving said carbon pile inwardlythereof, a magnetic circuit including a bottom plate, a core of magneticmaterial on which said solenoid is mounted having a portion projectingslidably through and beyond said bottom plate in the direction of saidtubular member, said projecting portion having engagement with saidtubular member for locating said member and said pile accurately withrespect to said solenoid.

19. In a carbon pile device, a solenoid, a pole piece for said solenoidat one end thereof, an armature for cooperation with said pole piece, acarbon pile, a tubular member for receiving said carbon pile inwardlythereof, means for mounting said tubular member adjacent and inalignment with said solenoid at the opposite end thereof from said polepiece, a core for said solenoid, and means forming an outwardlyextending projection on said core adapted to be received within saidtubular member for locating said member and said carbon pile in accuratealignment with said core.

20. In a carbon pile device, a piece for said solenoid at one endthereof, an armature for cooperation with said pole piece, a carbonpile, a tubular member for receiving said carbon pile inwardly thereof,means for mounting said tubular member adjacent and in alignment withsaid solenoid at the opposite end thereof from said pole piece, a corefor said solenoid, means forming an outwardly extending projection onsaid core adapted tobe received member for locating said member and saidcarbon pile in accurate alignment with said core, and an operating rodextending through said core from said armature and into said tubularmember for transmitting *essure from said armature to said pile.

21. In a carbon pile device, a solenoid, an armature for said solenoid,a carbon pile, a tubular member for receiving said carbon pile inwardlythereof, a core of magnetic material on which said solenoid is mountedand extending axially solenoid, a pole in the direction .of said tubularmember, means forming a projection onsaidcore adapted to engage withsaid tubular member for. locating said member andsaid pile accuratelywith respectto said solenoid, a contact member for making electricalcontact at one end of .said carbon pile, and means associated with said.contactmemoerand interfitting with said tubular member for locatingsaid contact member in predetermined position with respect to said pile.

22. A magnetic deviceincluding a core and. a pole piece in the .form ofa body of magnetic material including a radially inner portion and aradially outer portion-separated therefrom by an .intermediateannularportion of non-magnetic material, said poles piece being .secured tosaidcore and being, faced off to form aunirormly plane workingiaceflextending across said inner and outer magnetic portions and saidintermediate non-magnetic portion inaccurate perpendicular relation tothe axis of. said core.

23. The, method of .iorming. a magnetic device including a core and apole. piece inlthe form of a body of magnetic material includingaradially inner portionand a radially outer portion sep-, aratedtherefrom by an intermediate annular portion of non-magneticmaterialwhieh comprises the steps. of securingsaid pole ,piece to sa id.core, and thereafter facing offsaid pole piece including the surfaceof.said inner and. outer magnetic portions and said intermediatenon-magnetic portion to form a uniformly plane working face in accurateperpendicular relationto the axis of said core.

24. A magnetic device including a cOreand a pole piece inithe form of abodyof magnetic material including a radially innerz portion and aradially outer portion separated therefrom* by an intermediate annularportion of non-magnetic material having a tapered cross section increasing in the direction away from a working face thereof, said pole. piecebeing secured to said core and being faced off to form a uniformly planeworking face extending across said inner and outer magnetic portions andsaid intermediate non-magnetic portions in accurate perpendicularrelationlto the axis of said core, the depth of the facing-cutdetermining the minimum extent ofthe non-magnetic gap between said innerand outer portions.

25; A: magnetic device including a core and a pole piece in the form ofa body of magnetic material including a radially inner portion and aradially outer portion separated therefrom by an intermediateannular'portion of non-magnetic material. having a-xtap'ered crosssection increasing in the direction away from a working face thereof,said pole piece being secured to said coreand being faced off to form auniformly plane working face extending across said inner and router.magnetic portions and said intermediatenon-magnetic portions in accurateperpendicular relation to the axis of said core, the depth of saidfacing .cut determining the minimum amount of non-magnetic gap betweensaid inner and outer portions.

References Cited in the file of this patent

